WEST VALLEY CITY — Family and colleagues remembered a fallen Draper police sergeant during a public funeral Friday as a kind man with a passion for his work and his young family.

About 5,000 people — mostly police officers from the area and their wives — filled the Maverick Center in West Valley City to honor Sgt. Derek Johnson, 32, who was killed while on duty early Sunday. Police believe he was killed by a transient man who also shot himself and his girlfriend. No charges have been filed.

With Scottish bagpipes leading the way, Johnson's three brothers and other family members carried his body into the arena in a casket wrapped in an American flag as officers stood in salute. Johnson's wife, Shante Sidwell Johnson, walked slowly behind the casket holding their 7-year-old son, Bensen. The young boy, dressed in a black suit, hugged his mom tightly with his head buried in her shoulder.

"Derek loved Shante, Bensen and his family so much," said Draper police Sgt. Pat Evans, the best man at Johnson's wedding. "He always talked about them."

Family and friends said Derek Johnson always wanted to be an officer, practicing as a child by handcuffing his siblings to dressers and listening constantly to a police scanner as a teenager. His brother, Darin Johnson, said his commitment to public safety likely led him to check on a car parked oddly on a street, an act that triggered the shooting, police say.

"You could have just drove by, wrote that car off," Darin Johnson said. "But you stopped to assist as the humble servant that you are. In a moment, you were taken from us and my heart bleeds."

Gov. Gary Herbert said Johnson represents the "best that our communities have to offer," and encouraged the audience to emulate the giving spirit that Johnson embodied. His siblings said Johnson was always smiling and could light up the room.

"I can't wait to laugh with you again," said Darin Johnson.

A member of The Church of Jesus Christ of Latter-day Saints, Johnson was remembered by Mervyn B. Arnold, a member of LDS quorum of the seventy, as a giving man who wanted the best for others, and made others smile and laugh.

Police believe Timothy Walker, 35, fatally shot Johnson early Sunday after the sergeant stopped to investigate a Volvo parked along a road. The full details of what happened have yet to be released publicly, but police have said that Johnson was ambushed — shot while in the seat of his patrol car before it crashed into a tree.

Charges have not yet been filed against Walker, who was upgraded on Thursday to serious from critical condition.

Walker's longtime girlfriend, Traci Vaillancourt, 34, is in fair condition and has spoken with investigators. Based on those conversations, investigators still believe she is a victim, Unified Police spokesman Justin Hoyal said.

Outside the arena in West valley City, a Salt Lake City suburb, hundreds of American flags lined the parking lot, and blue ribbons hung from the railings of the stairs. Dozens of framed photographs of Johnson with his wife, son and siblings were on display on tables inside the arena.

In one photo, Johnson held his son with both of them wearing matching Superman T-shirts — each with huge smiles on their faces. Another photo showed him and his wife on their 2000 wedding day at the Mormon temple in Salt Lake city.

His passion for his work was also on display: In one picture, Johnson stood beaming in front of his Draper police patrol car. A small plaque read, "Land of the free because of the brave."

Johnson's family said the Utah native loved being a public servant. He became a full-time officer in Draper in 2004 and was promoted to sergeant in 2012.

Johnson was the first officer killed in the 11-year history of the Draper police department. Draper is a city of 44,000 about 15 miles south of Salt Lake City.

He was the first Utah law enforcement officer killed since Utah Highway Patrol Trooper Aaron Beesley died in June 2012 after falling from a cliff during a search and rescue mission near Mount Olympus. The last officer gunned down was Ogden Officer Jared Francom, who was shot during a drug raid in January 2012.

Following the funeral service, Johnson's body was taken in a motorcade of police cars and fire trucks for burial at a cemetery in Sandy.